// 二进制求和
class Solution {
    public String addBinary(String a, String b) {
        StringBuffer ret = new StringBuffer();
        int cur1 = a.length() - 1;
        int cur2 = b.length() - 1;
        int t = 0;
        while (cur1 >= 0 || cur2 >= 0 || t > 0) {
            if (cur1 >= 0) t += a.charAt(cur1--) - '0';
            if (cur2 >= 0) t += b.charAt(cur2--) - '0';
            ret.append((char)((char)t % 2 + '0'));
            t /= 2;
        }
        ret.reverse();
        return ret.toString();
    }
}